The following description relates to devices for detecting bacteria and more specifically to the use of phage or phages to detect bacteria.
Phages are viruses whose hosts are bacterial cells. The phage identify their hosts through specific receptor molecules located on the outside of the host cell. Once the phage find their specific receptors, they bind to the bacterial cell and inject their nucleic acid into the cell. This makes it possible to use phage to detect bacteria and, because phage binding can be so selective, it is possible to use phage to detect specific strains of a single bacterial species. For example, wildtype phage T4 can infect both E. coli strains B and K12 but a rII mutant of phage T4 will only infect E. coli strain B. Thus it is possible to ferret out a single bacterial strain among several strains.
Whiles antibodies have also been used to discriminate bacterial species, there are a number of advantages to using phage in place of antibodies. Antibodies are bare protein molecules. As such, they can potentially be a food source for bacteria, leading to false alarms (specificity errors) in antibody-based bacterial detection techniques.
Because many antibody-based field test kits are currently inadequate in ferreting out specific bacterial sources, the White House has advised caution in their use. This constraint has been imposed because false positives in the past have resulted in buildings being unnecessarily shut down and antibiotics being unnecessarily dispensed. Other limitations of such antibody-based immunoassays include antibody manufacturability and instability.
Phage on the other hand is widely available and in fact libraries of phage exist. One such library is the Felix D'Herelle Reference Center for Bacterial Viruses at Laval University in Quebec, Canada. This library has a collection of approximately 500 phages.
Phage is also very robust, and is not as sensitive to temperature, pH, and ionic strength as antibodies are. Once a phage for a given host has been identified, large quantities of phage can be easily manufactured and purified. The purified phage exhibits a long shelf life.
The use of phage as a bacteria sensor can take a number of forms. Phage can be coupled to magnetic microparticles that are in turn used to capture the host bacteria from an aqueous/air environment. Once captured, a magnet can be used to separate the captured bacteria from the rest of the sample matrix and to concentrate the captured bacteria onto an optical surface for detection.
Phage can also be coupled to optical fibers, glass, polymers, and quantum dots. In all such applications, a reliable method is needed to orient and bind the phage to these different substrates so that the phage can be effectively used as a bacteria sensor.